Graphene, a two-dimensional (2D) single layer of carbon
atoms, is a rapidly rising star on the horizon of materials
science and condensed-matter physics.
It has attracted tremendous attention because of
its unique massless Dirac fermion-like electronic properties
[1]} and potential applications
in electronic devices. [2]}
When graphene is etched
or patterned along one specific direction, a novel
quasi one-dimensional (1D) structure, a strip of graphene of nanometers
in width, can be obtained, which is referred to as
a graphene nanoribbon (GNR). The GNRs are predicted to
exhibit various remarkable properties and may be a potential
elementary structure for future carbon-based nanoelectronics.
[3]}, [4]}, [5]}, [6]}, [7]}
Remarkably, theoretical calculations [8]}, [5]} predicted that quantum
confinement and edge effects make narrow
GNRs (width w \(<\)  10 nm) into semiconductors,
which differs from single-walled carbon
nanotubes that contain some metallic
species.
Thus, GNRs with narrow widths and atomically smooth edges could be
used as room temperature field
effect transistors with excellent
switching speed and high carrier mobility
(potentially, even ballistic transport).
Indeed, Li et al. [10]} recently produced GNRs with width below 10 nm
using a chemical route and found that all of the sub-10-nm GNRs
were semiconductors and afforded graphene field effect transistors
with on-off ratios of about \(10^7\)  at room
temperature.[10]}, [12]} Unfortunately,
the yield of GNRs was low and their width distribution was broad;
widths ranged from less than 10 nm to \(\sim \) 100 nm
